I highly recommend doing a gap year, and no, adcoms don't frown on them at all. Not only is dental school different and more challenging and time consuming than undergrad, but once you're out you'll be practicing and finding time to get away will be much more difficult. Go backpack across Europe, do a few roadtrips, work in something you find interesting and not what you think an adcom would "want to see" (i.e. bent over a test-tube, dental assisting, etc.). Soak in some fun and get as many kinks and wild oats out of your system before jumping back into the fire. You'll be the better for it, trust me.😉